Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of both gaseous and solid material, such as, for example, particulate matter. Particulate matter may include ash and unburned carbon particles and may sometimes be referred to as soot.
Due to increased environmental concerns, exhaust emission standards have become more stringent. The amount of particulate matter and gaseous pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. In order to meet these emissions standards, engine manufacturers have pursued improvements in several different engine technologies, such as fuel injection, engine management, and air induction, to name a few. In addition, engine manufacturers have developed exhaust after-treatment systems to treat the exhaust gas after it leaves the engine.
Engine manufacturers have employed exhaust after-treatment devices called particulate filters or particulate traps to remove the particulate matter from the exhaust flow of an engine. A particulate trap may include a filter designed to trap particulate matter. The use of the particulate filter for extended periods of time, however, may enable particulate matter to accumulate on the filter, thereby causing damage to the filter and/or a decline in engine performance.
The particulate traps may be combined with oxidation catalysts to decrease the temperatures at which oxidation of NO takes place and to promote formation of CO2 out of the particulate matter. Such oxidation catalysts and particulate filters may be contaminated, for example, when the wrong fuel is supplied to the engine. For example, in a diesel engine assembly the diesel oxidation catalyst may be contaminated when a diesel fuel containing a significant amount of sulfur is used. Contamination should not be confused with a high soot load level. A high soot load level may normally be solved by regeneration of the after-treatment system that may be done at relatively low temperatures. Contamination is a situation in which the oxidation catalyst may have become inoperative or less effective so that the regeneration at the relatively low temperatures may not be effected anymore. It is a challenge to de-contaminate a contaminated after-treatment system.
The present disclosure is directed, at least in part, to improving or overcoming some aspects of known after-treatment systems.